Because the child's legal custody belongs to the child's parents, grandparents can't directly claim the child's custody unless the parents are dead or unable to support them or there are other legal reasons. It is not illegal for in-laws to rob children of custody.
First of all, parents have written to their children's legal guardians, and others have no right to interfere. When the father of the child is alive, the grandparents of the child have no right to seize the custody of the child. But if the child's father dies, then the child's grandparents can fight for custody. Generally, children under two years old are brought up by their mothers. The ownership of custody should be based on the premise that it is more conducive to the physical and mental health of children. The issue of custody is limited to the child's guardian. Divorce usually leads to the loss of custody of one of the spouses. The party who loses custody will lose the right to live with their children.
Legal basis:
civil law
Article 1084 The relationship between parents and children shall not be destroyed by the divorce of parents. After the divorce, the child is still the child of both parents, whether or not the parents directly raise him. After divorce, parents still have the right and obligation to raise, educate and protect their children. After divorce, children under two years old are directly raised by their mothers. For a child who has reached the age of two, if both parents fail to reach an agreement on the issue of support, the people's court shall make a judgment based on the specific circumstances of both parties and the principle of being most beneficial to the minor children. Children over the age of eight should respect their true wishes.